1. Field of the Invention
One or more aspects of the present invention relate to a load-control backup signal generation circuit which supplies a backup control signal to a load switch connected to an output of a control processor, in a case in which a malfunction occurs in the control processor which operates according to a predetermined program.
2. Description of the Related Art
For example, a microprocessor for control which operates according to a predetermined program, that is, a microcomputer (control processing unit) (CPU) is embedded in various electronic control units (ECU) that are mounted in a vehicle.
The microcomputer generally performs various controls according to the content of a program that is prepared in advance, as scheduled. However, for example, in a case of being influenced by electromagnetic noise entering from the outside, a case in which a microcomputer fails, a case in which an unexpected operation is performed due to the influence of defects (bug) included in a program itself, or the like, the microcomputer can be in a runaway state.
If the microcomputer is in a runaway state, the entire electronic control device is in an uncontrollable state. Thus, a system of various electronic control devices monitors whether or not a malfunction occurs in the microcomputer, and in a case in which an occurrence of a malfunction is detected, it is necessary to return the microcomputer to a normal state.
For this reason, various electronic control devices of the related art control in such a manner that the microcomputer periodically outputs a pulse called a watchdog signal to the outside. Then, a monitoring circuit is connected to the outside of the microcomputer, and the monitoring circuit constantly monitors a watchdog signal that is output from the microcomputer. If a malfunction occurs in the microcomputer, the watchdog signal no longer appears. If the monitoring circuit detects a state where the watchdog signal does not periodically appear, an operation of the microcomputer is initialized.
In an in-vehicle electronic control device described in JP-A-2010-13988, if runaway of a main CPU 10 illustrated in FIG. 1 occurs and a pulse width of the watchdog signal WDS becomes excessive, a power supply control circuit 113 detects this and generates a reset pulse signal RST.
In addition, also in an electronic control system for vehicle described in JP-A-2011-98593, a watchdog timer 24 that is embedded in a power supply control IC 23 monitors an operational state of a CPU 1 based on a watchdog signal that is transmitted from the CPU 1, and when a malfunction occurs, transmits the reset pulse signal RST.